Considering the excessive amount of and many kinds of respiratory disorders and symptoms, in the other side the doctor’s memory for remembering all kind of respiratory disorders and symptoms is very restricted, so it is needed an expert system as an auxiliary tool for the doctor in diagnosing a disease based on its symptoms. The diagnose result will become a basis of medicine usage on patient as medical treatment. In this case the specialized knowledge base of this expert system was built from the interview with doctors, reading books, journals, and studying from previous researches. The developed inference engine was built using forward chaining method and having certainty factor for reasoning under uncertainty. The technique of resolution conflict uses sequence of the rule that is arranged based on symptoms priority of certain disease diagnosis and the choice will trigger the first active rule that is rule with highest
priority. The expert system has been able to diagnose of the diseases and has given suggested therapies for patients. It also facilitates knowledge base development and has explanatory facility menu in which its interface is more user friendly.